Effects of additives on the discharge behaviour of positive electrodes in lead/acid batteries

The effects of expanded graphite, carbon fibre, needle coke and polyacene, when used as positive electrode additives, on the PbO2 electrode behaviour of lead/acid batteries are studied. It is found that, during the initial stage of charge/discharge cycling, all of the additives are able to raise appreciably the coefficient of utilization of the positive active material. By contrast, they cause, to differing degrees, a reduction in service life when a certain nitrogenous heterocyclic compound (AS) is added to the positive active material. The coefficient of utilization of the latter is increased greatly during deep cycles. The addition of the graphite-AS composite additive improves the coefficient during the total period of cycling and reduces the consumption of lead powder in the PbO2 electrode by 14%. It is also found that the addition of 1 wt.% of Li+ to the electrolyte has a beneficial effect on the discharge capacity of the positive electrode. When lithium sulfate is added to the lead paste, together with the graphite-AS composite additive, the results show that not only the superiority of the positive electrode can be maintained, but also the service life is not less than that of any positive electrode with the additive of graphite, AS, or graphite-AS composite additive.